The present invention relates to the reactivation of fluid bed catalysts. In particular, the present invention relates to on-line, in situ reactivation in reactor standpipes of fluid bed catalysts used in the petroleum, petrochemical and chemical processing industries. More particularly, the present invention relates to on-line, in situ reactivation in reactor standpipes of fluid bed oxidation catalysts useful in the preparation of maleic anhydride from C.sub.4 hydrocarbons, including n-butane.
Maleic anhydride can be produced by oxidizing hydrocarbons, such as butane, butene, butadiene and benzene. Oxidation catalysts containing the mixed oxides of vanadium and phosphorus have been utilized to produce maleic anhydride from C.sub.4 hydrocarbons, such as n-butane. It has been observed that as the time of reaction on the catalyst increases, the yield, activity and selectivity of the catalyst decreases. This is called "catalyst aging" or "catalyst deactivation", and is common in most catalytic processes.
The reduction in maleic anhydride yield means that more of the hydrocarbon feed is fully oxidized to carbon oxides and water; that total production of maleic anhydride declines; increased unit cost of the maleic anhydride produced; and relatively frequent catalyst replacement. Skilled workers in the art have suggested various methods of countering this loss of catalyst performance.
British Patent Specification 1,439,489 discloses regeneration of a phosphorus-vanadium-oxygen complex catalysts by discontinuing the butane feed and treating the catalyst with a reducing material such as hydrogen, carbon monoxide, methane, hydrogen sulfide, or mixtures of the same. In U.S. Pat. No. 4,123,442, sulfur trioxide was employed to partially regenerate the catalytic properties of an aged maleic anhydride catalyst. U.S. Pat. Nos. 4,020,174, 4,089,807 and 4,094,816 disclose the use of halogens or organic halides as useful in regenerating vanadium-phosphorus catalysts. U.S. Pat. No. 4,178,298 describes activation and regeneration of fixed-bed oxidation catalysts using gaseous hydrocarbons. British Patent Specification 1,512,305 describes regenerating complex phosphorus-vanadium-oxygen catalysts by treating the aged catalyst with an aqueous solution of ammonia or amine at an elevated temperature. Many the methods described above require the removal of the deactivated catalyst from the reaction system, and all the methods require significant disruption of the production process. No known prior art describes reactivating catalyst in a fluid bed reactor standpipe.